The present invention relates to safety switches for electric lamps. More specifically, the present invention relates to safety switches designed to turn off or reduce the power to the bulb of a lamp in order to avoid a hazardous condition.
It has been recently recognized, especially with the increased use of halogen lamps, that lamp bulbs, which produce a significant amount of heat in addition to light, can present a fire hazard under certain non-standard use conditions. Safety standards, providing performance criteria, include measuring the temperature profile of a lamp when covered by a flammable foreign object, cloth or material and the ability to avoid a hazard if tipped over must be met by current lamps.
Lamps, especially vertically oriented lamps such as floor lamps, table lamps and torchiere style lamps, can be tipped over or knocked off of tables. If the bulb and/or its surrounding structure comes in contact with flammable material such as carpet, upholstery or drapes, a potential fire hazard is created. Even after a lamp is tipped over, the bulb will continue to be supplied with electricity and will continue to generate heat, contributing to the fire potential. If the bulb breaks, an electrical hazard is also created.
Many lamps, including halogen torchiere lamps are commonly equipped with electronic dimmers. The fundamental component of such a dimmer is a triac. Many different control circuits have been invented to mate with a triac. One circuit is a phase-cut control circuit that comprises a potentiometer, a capacitor and a trigger diode. China Patent CN 94 213163.0 discloses a type of such a control circuit.
It can be desirable to further control the phase control circuit in order to reduce the power consumption and heat generated by halogen lamps. Therefore, in addition to the simple phase control circuit, including the triac, the potentiometer, the capacitor and the trigger diode, an additional electronic control circuit can be added.
Control circuits used to control the typical triac dimmer have been disclosed. In U.S. Pat. No. 4,751,433 a photocell is used to make the luminous energy emitted from the lamp inversely proportional to the luminous intensity of the surrounding space. The critical point (action point) of this control device is set by the manufacturer, therefore, the consumer is unable to reset or adjust the device. In U.S. Pat. No. 4,658,129, a photoelectric sensing unit is used to deliver an output voltage in response to changes of the intensity of light. The output voltage is applied to a capacitor for operating an SCR in order to automatically control the ON/OFF status of the lamp.
If one room has light-colored furniture and ceilings and another room has dark-colored furniture and ceilings, the same halogen torchiere lamp placed in both rooms with the same power output, for example, 300 Watts, will cause quite different surrounding brightness. If the "action point" had been pre-set by the manufacturer, no adjustment can be made by the customer himself. The auto-control device of existing halogen torchiere lamps will be triggered at inappropriate times in both cases.